The present invention is useful for monitoring operating environments, and in particular, to instrumented components and telemetry systems enabled for wirelessly transmitting electronic data indicative of individual component condition within an ultra high temperature operating environment such as that of a combustion turbine engine. One such system is described in pending U.S. patent application Ser. No. 11/936,936 filed on Nov. 8, 2007, published as United States Patent Application Publication 2009/0121896 A1 on May 14, 2009, attorney docket number 2007P20938US, incorporated by reference herein.
The usual range of operating temperatures for transformers is from ambient to 200° C. However, optimization of current industrial processes requires that equipment sensors operate reliably and receive and transmit electrical power and signals in temperature conditions from ambient to temperatures which exceed 200° C. Depending on the specification and configuration of the electrical power source and signal transmission pathways required, transformers may form part of the instrumentation circuitry and/or can be used to adjust and transmit frequency and voltage as require for a particular use.
When wires cannot be routed directly from the outside to sensors inside a containment vessel of an industrial process, such as a gas turbine engine, transmission of power and/or data is induced across a gap to maximize reliability and reproducibility. To effectively transmit power and/or data across a gap, a primary coil on one side and a secondary coil on the other side are used. The power and frequency sent through the primary coil induces a power and frequency in the secondary coil to complete the transmission of an electrical signal. At efficiencies less than 100%, the amount of power induced in the secondary coil is less than the power provided through the primary coil. Materials presently used as transformer cores have a magnetic permeability, which degrades as the temperature increases into high temperature ranges, thereby reducing the efficiency of the power transmission through the transformer. For this reason, manufacturers of transformer cores do not rate their transformer core materials as being effective above 250° C.
FIG. 1 shows a conventional prior art closed core transformer 28. Primary circuit current flow 29 of an alternating frequency through the primary coil 30 having multiple windings creates an alternating magnetic field in the core 32. The alternating magnetic field is carried by the core 32 to the secondary coil 34 having multiple windings to create a secondary circuit alternating frequency current flow 33.
Russell G. DeAnna in his report on Wireless Telemetry for Gas-Turbine Applications (NASA/TM-200-209815)(ARL-MR-474) from the Glenn Research Center March of 2000 stated:                (page 8) “A reasonable goal for these telemetry systems is operation at a temperature up to 500° F. (260° C.). This would allow an uncooled package located outside the gas path in the compressor region. The transmitting package would have to be cooled in the combustor and turbine sections. Designing a telemetry system for operation at 260° C. and beyond will be challenging.        Karnani (1998) demonstrated wireless telemetry using inductive coupling of power and data at 392° F. (200° C.), and makes recommendations on high-temperature components such as capacitors, resistors, oscillators, and solder . . . . The variation of resistivity with temperature is the most important effect on resistors . . . . High temperature electronics failures are often due to packaging technology rather than the actual material employed or the electrical failure of the component.        Current telemetry systems use 1970's analog technology, require cooling below 257° F. (125° C.), and have limitations in accuracy and channel capacity. A new system should be digital and allow improved data quality and quantity, while allowing operation at higher temperature—at least 392° F. (200° C.)—in the hot gearbox oil where these systems are frequently located. The system would require shaft mounting. Since the telemetry system is rotating, sensors are usually hardwired to the telemetry system.        (page 10) High-Q circuits are desired to maximize power transfer. In wide-temperature applications, however, high-Q circuits are not the only goal because LRC components have temperature-dependent properties and the circuit can drift out of resonance if the circuit Q is too high. Hence, the circuit gain should be spread out over a larger band of frequencies in order to accommodate any frequency variation. Q equal to 23 was used by Karnani (1998) in a circuit designed to operate over a temperature range of 392° F. (200° C.). The low Q was obtained by using a transmitter coil with only two turns of copper.        A critical issue for gas-turbine applications is the proximity of the coils to magnetic materials like steel . . . . The system must therefore be designed so that the power coils are located as far as possible from steel, or else sufficient excess power must be available at the primary coil so that the losses can be tolerated. A ferrite core may be used in the secondary coil to improve efficiency. When using ferrite, however, the frequency dependence of the permeability must be observed to avoid possible saturation at high frequencies.”        
FIG. 2 is a schematic illustration of an air core transformer 40, with a ferrite core 37 in the secondary coil as suggested by DeAnna to improve transmission efficiency. Primary circuit current flow of an alternating frequency 36 through the primary coil 35 having multiple windings creates an alternating magnetic field in and around the primary coil 35 which induces an alternating magnetic field in the ferrite core 37 and the secondary coil 38 having multiple windings surrounding the ferrite core to create a secondary circuit alternating frequency current flow 39.
There still exists a need to power ultra high temperature electronics reliably and repeatably while reducing or eliminating the variations in electrical circuit characteristics due to temperature changes for temperatures exceeding 200° C.